android-first-line/app/src/main/java/pers/tanyong/hello/MainActivity.java
<filename>android-first-line/app/src/main/java/pers/tanyong/hello/MainActivity.javapackage pers.tanyong.hello;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button button = findViewById(R.id.button3);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent();
                intent.setClass(MainActivity.this, MainActivity2.class);
                startActivity(intent);
            }
        });
    }
}
